1. Field of the Invention
The present invention relates to LED lamps and more specifically, to a collimating lens for LED lamp.
2. Description of the Related Art
FIG. 5 shows a conventional collimating lens 90 used with an LED lamp 98. The collimating lens 90 has a top face 92, a bottom face 94, and a sidewall 96. An accommodation hole 942 is formed on the bottom face 94 for accommodating the LED lamp 98. The sidewall 96 has a first wall section 962 and a second wall section 964. The first wall section 962 obliquely upwardly extends from the bottom face 94 and connected to the bottom side of the second wall section 964. The second wall section 964 extends vertically upwards from the top side of the first wall section 962, and is connected to the top face 92 at right angles. The first wall section 962 and the second wall section 964 define a contained angle greater than 180°. When the LED lamp 98 is turned on to give off light, radially emitting light rays from the LED lamp 98 are repeatedly refracted between the top face 92 and sidewall 96 of the collimating lens 90 and finally sent out of the collimating lens 90 through the top face 92 in direction approximately perpendicular to the top face 92. Therefore, the collimating lens 92 concentrates the light of the LED lamp 98 into a directional light beam.
According to the aforesaid design, the first wall section 962 and the second wall section 964 define a contained angle greater than 180°. When the top face 92 refracts the light of the LED lamp 98 onto the second wall section 964, a part of the refracted light passes through the second wall section 964 due to excessively big incident angle, causing dispersion of light source and lowering the illumination performance of the lamp.